Even though the wireless communications were initially developed to provide voice services, technologies for providing data services have been developing according to rapid technological improvements. Furthermore, as the demands for data transmissions and the number of mobile stations are increasing, technologies have been developing for more efficiently transmitting data. Such a wireless communication system allows every mobile station to more exactly grasp channel conditions between a base station and the mobile station and then transmit data.
The Wideband Code Division Multiple Access (WCDMA) communication system transmits data of all users by spreading it over the entire bands, so that there is only a channel quality value and data transmissions, the mobile station initially acquires control information such as the number of times of retransmission responses, a feedback period of the channel quality value, the number of times of repetition transmissions of the channel quality value, power offset, and the like, through signaling with a base station. A mobile station to carry out communications continues to monitor an entire High Speed Shared Control Channel (HS-SCCH), periodically transmitting a channel quality value through a High Speed Dedicated Control Channel (HS-DPCCH). Further, if the mobile station finds out control information necessary for data reception, the mobile station receives data based on the control information through a forward High Speed Packet Data Shared Channel (HS-PDSCH).
In the meantime, discussions on the Long Term Evolution (LTE) are in progress in the 3rd Generation Partnership Project (3GPP) which is responsible for standardization. The LTE is a technology for implementing high-speed packet-based communications of about 100 Mbps for the purpose of commercialization by year 2010. The Orthogonal Frequency Division Multiplexing Accessing (OFDMA) technology is currently considered for the LTE.
The OFDMA technology, as a data transmission technology using multi-carrier, refers to a technology for converting symbol sequences inputted in series into symbols in parallel and modulating and transmitting the symbols by using a plurality of orthogonal sub-carriers.
The OFDMA system requires channel quality indicator (CQI) fed back by a mobile station in order to more adaptively allocate and employ wireless resources according to wireless environments of mobile stations under consideration of wireless resources efficiency. Such channel quality indicator feedback is implemented through a control channel shared by several mobile stations.
For example, a mobile station in the OFDMA system measures selected parameters of a received signal. Furthermore, the parameters measured at the mobile station and estimation values obtained from selectively measured parameters are fed back to a base station through a standard message referred as a channel quality indicator (CQI). Next, the base station uses CQI information to optimize signals transmitted from a forward channel, so enhancing signal receptions at the mobile station.
In general, since a characteristic of a wireless channel varies with time, the variation of channel quality has to be fed back to a base station in order to maintain optimal performance when the channel quality variation occurs. However, the feedback of channel quality indicator should be carried out under consideration of other users and loads caused by using uplink resources for performing the feedback operation.
To do so, in the conventional approach, each mobile station compares a channel gain of received signals to a predetermined threshold value, and feeds back channel quality indicator through a feedback channel to a base station only when the channel gain is higher than the predetermined threshold value. The predetermined threshold value is applied to all mobile stations in the same manner.
Under real wireless environments, a mobile station typically has a reception power level different from that of another due to a distance between a mobile station and a base station, and geographical communication environments in which a mobile station is placed. However, when the same threshold value is assigned to all users and the feedback of channel state information is made according to a result of comparison of an estimated channel gain and one threshold value, there is a problem that a mobile station of highest reception power level, e.g., a mobile station closes to a base station, can easily feed back channel quality indicator while a mobile station of low reception power level, e.g., a mobile station located far away from a base station, can hardly feed back the channel quality indicator. As a result, according to the conventional approach, there occurs a problem of fairness on user capacity within the same cell, which can become more severe as a reception power level difference of users becomes bigger.